I didn't download your site, so I have no idea what is in your *.js file. What I did learn, however, is that you do not have "document.all" within the main file -- and in all likelihood, no 'document.layers'. So...
...ie5+ & nn6 code goes here...
else if (document.all)
...ie 4+ code goes here
else if (document.layers)
...nn4 code goes here...
elementby & all use '.style'; nn4 does not
if you need more see the "dHTML: an Introduction" script/tutorial at my site (GrassBlade)